The cross between the progeny of F1 (that is F2 generation) and the homozygous recessive parent is called Test cross.
This was a method discovered by Mendel which was useful to identify the genotype (genetic makeup) of a plant whose phenotype (visible expression) is known.
For example consider a tall plant from F1 orF2 generation can have either TT or Tt as its genotypic composition. Mendel crossed the tall plant from F2 generation whose genotype is to be determined with a dwarf plant (homozygous recessive – tt). And then he concluded that:
• if all the plants obtained from test cross are showing same phenotype (for example: all are tall) then the unknown tall plant is homozygous dominant in genotype(TT)
• if all the plants obtained from the test cross are showing different phenotype(for example: half are tall and half are dwarf plants) then the unknown tall plant is heterozygous in genotype(Tt).
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